Update:
In addition to the arrival of my ordered Hall effect sensors, I have also acquired a very painful shoulder injury (yay!), which is going to slow down the development of this project's hardware slightly (although thankfully, the mechanical stuff is almost finished). Once the wood, nails and paint part is finished, then the rest is software which should forge ahead at full steam! I have a good idea of the final mechanical form and it's quite straight-forward.
So tonight, I wired up a Hall sensor (
https://www.bitsboxuk.com/index.php?main_page=product_info&products_id=3392) on a breadboard and measured it's performance on my scope. Picture below.
Sensor works like a champ. It shows no sign of problematic noise when I
slowly turn the ring gear by hand. And the hysteresis pattern is nice and wide. I'll place the sensor just ahead of the "zero" bit so the CPU can calibrate itself during startup.
In the photo, the hall sensor is held temporarily in place with blue tape, and a small neodymium magnet is blu-tac'd into the gear teeth just to the right of the sensor. The sensor's output is shown on the scope in the background.
Thanks to Kleinstein, jpanhalt and PCB.Wiz for your comments:
I am going to make a new 8-tooth gear rather than fix it in software, because I like making stuff on my scrollsaw and I don't like software kludges.
Regarding the "halflife" of the glow material - I can't measure that accurately right now for many reasons, but I will do so in a scientific manner and share the results with you all at a later date (maybe the weekend hopefully?).
This glow powder is quite amazing actually. Last night at about 2am I awoke and saw that the ring gear sat forlorn on my bench was almost entirely dim. So I grabbed my flashlight and hit 4 of the bits from point blank range with a very short blast of bright light. Immediately, the small room was subtly illuminated with a faint green glow!
Four hours later I could still tell which 4 bits they were! Not scientific at all but fun to know.
I am optimistic about a good result from this project! Stay tuned.